The as-yet-unnamed colt, who shares Black Caviar's mother, or dam, Helsinge, was bought by Australian bloodstock firm BC3 Thoroughbreds for A$2m (£1.4m) more than the previous record.
BC3 Thoroughbreds purchased Black Caviar's half-sister Belle Couture for A$2.6m (£1.8m) at the same sales last year, while a third Helsinge progeny, three-year-old colt All Too Hard, has already won three Group One races.
Black Caviar, who was bought by trainer Peter Moody for A$210,000 (£143,000) at the Melbourne yearling sales in 2007, is scheduled to go for her 25th win in as many races on Saturday at Randwick racecourse, next door to the venue of the sale.
Moody, who has said Black Caviar will not run in the T.J. Smith Stakes if the going is heavy, was impressed by the six-year-old mare's half-brother.
"He's like poetry in motion when you see him move," he told ABC. "Every muscle moves at the right time with the next one.
"When you see Black Caviar when she moves, you can see he's inherited a lot of that athletic ability that she's got."
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